Triggers of Dive Accidents

[danvolker]

Yes, reducing risks is the point of this discussion! Yet you are either being perplexingly single-minded about the least-pressing risk: not having (gobs of)surplus air when atmospheric air availability is a virtual certainty, or you have access to knowledge of the physiological risks (safety stop is optional, O2 on the boat is superior to in-water off-gassing - the humiliation of the diver being just a bonus I'm assuming) that is so certain that you're able to advise any other diver that planning for rare and inconsequential contingencies, or minor convenience, should absolutely take precedence. No question, insane not to... Yet just a post or two earlier you gave thanks to a painstaking elaboration about the individuality and noteable unpredictability of DCS, as well as mentioning it yourself.

Why is it not the better plan to give yourself as much opportunity for off-gassing? Frequent assertions are made here about the risk of not getting your ass right to the surface, yet no credible risks have been articulated. Absent some certainty about how to view nuances of DCS risk, how are you making your assessment?

For a great many new divers, 500 psi at 60 feet down will be almost gone by the time they are 1 minute into their 15 foot stop. For these divers, a serious risk is OOA.
DCS from a 60ft for 45 min dive should not be a risk if they just swim up slowly with no stop. On one hand we have a big risk. On the other, we do not.
I don't see how this makes my posting seem single minded...

The tables a new diver will use, are extremely conservative....so much so, they could actually cause a dramatic increase in danger for a fit technical diver....there is so much fudging tossed in for low fitness levels and PFO issues, that they can make a fit diver have to do deco for his deco....ie, drastically less time should be spent by this diver at most stops on deep dives of long duration.
Point being, your individual off gassing is your big issue to learn...
If I am going to give advice on this issue here, it is the dcs issue is small risk to the 75 percent of divers with no PFO.....for the 25 percent that does have a pfo, your medical problem should not have been figured into the tables, compromising the people without pfo's. I would like much more individualized tables for divers, like what the WKPP has, but that won't be happening.....


Also.....

Who is teaching that safety stops are mandatory? When you have lots of air, they are smart. When you are really low on air, they are not related to safety anymore.

Regards
DanV

 

[Ayisha]

Hi there, the common saying used to be to "be back on the boat with 500 psi". Of course, we didn't really know what pressure we should start ascending at to achieve that unless we asked or figured it out. Starting your ascent at 500 psi, as you're saying above, is giving you even less reserve if you're deep enough to plan a safety stop. Starting your ascent at 500 psi would be fine on a shallow dive, but you might want to consider beginning your ascent much earlier on deeper dives in case you or your buddy have issues and need more air. You can search "rock bottom" or look at Lamont's signature to figure out how to calculate what your turn pressure and reserve should be depending on the type of dive you're doing and apply it to your own type of diving. My buddy and I usually start ascending from deep dives once the first one hits1000 psi. If we have to get back to an ascent line before that, we will usually start heading to the line at around 1300 - 1500 psi, depending on how far it is. We will then do a deep stop about half way and a slow ascent plus an extended safety stop.

You should plan to do a safety stop for deeper dives. You may want to look into the research on deep stops as well for deeper dives.

Keep reading, keep learning. Most of us probably dive differently than when we first started. I know that I've become more conservative as I go along and with all the info I read on this board and others.

(Based on your comment) Should I infer that the SS for OW divers with a max of 60 fsw is not really needed then it's possibly over stressed in the OW class.

Is that inference based on my comment or someone else's? Please don't infer from my post to skip any safety stop you feel you should make. My post followed Dan's original post saying that you should have skipped the safety stop. My personal feeling is that I will make any safety stop that I have planned, providing that I have the gas to do it. By the same token, I also make sure that I ascend with a sufficient gas reserve for any dive that I do. I am normally back on the boat with over 1000 psi, and that is diving almost to the NDL's on an AL 63, making a deep stop and extended safety stop. I plan my dives slightly less conservatively as you can read in my post above, but we usually hit close to the NDL before we reach our turn pressure.

I did not learn in my OW course to make safety stops for dives less than 60 feet, and was not taught to do a safety stop until the deep dives (over 60 feet) of the AOW course 3 months later. I did read later in the basic book about safety stops being recommended on all dives, but it was not stressed in O/W class. Do I do SS's on a 30 foot dive? No, because I haven't gone anywhere near the NDL. Most of the dive is a safety stop. Will I do a SS on a 55 foot dive? Sure. Even shallower, my computer will require it, and I have no problem with that. If you have the gas, the safety stop is not going to hurt you, but it can help you. If you plan correctly, have good situational awareness, have good gas management skills, stay right beside your buddy and follow a plan that you have made, then you will have enough gas to complete an extended safety stop or any ascent rate or any deep stop that you have planned, even if you had an emergency situation. If you've planned for all that, surely you will have enough gas to make a safety stop? Do whatever you feel that you should do for the type of dives you're doing.

 

[Freezerbrn]

@Ayisha I was just seeking clarification. I follow the computer (Sunnto Cobra) recommendations on my dives for NDL and stops. I have it set to be a little more conservative due to cold temps and my age so I feel comfortable when planning. The them of my post was what was being taught and what I felt the additional emphasis on gas management during OW class. My last few dive were on a steel LP95 at 70 fsw. I got closer to NDL long before I I reached a turn around point on gas.

Thank you for you advice, I appreciate help.

 

[spoolin01]

DanV,

We do see this differently. Here's my take on your risk management algorithm:

DCS - no BIG risk, ergo... no risk at all

[-]OAA[/-] less than excess reserve at the surface - some (unspecified) HUGE risk, so this dominates once some minimum time for off-gassing is satisfied.

I hope new divers will quickly figure out that they can safely address both, and to what extent reserving gas is needed for their safety.

I'm no expert on the state of DCS understanding but the stuff you mention that implies any precision or accuracy to the foreseeability of personal risk does not fit with what I do (think I) know. Though I'm sure I'm not doing it justice, my take is that the current models come from "start with 1% acute clinical DCS risk, take a step or two to the happy side, throw in some animal and tissue studies of difficult-to-place relevance, a lot of pontificating and presumptive tweaking, express it precisely so it seems definitive, and there you have it". Virtually no data on lesser endpoints than acute DCS. That doesn't give me much confidence that the entire exposure space between there and never crossing below the surface is properly or prudently defined as 'safe', meaning without adverse consequence. It seems there's plenty of evidence that could mean a continuum and even accumulation of the harm, and to my logic that means shade to the conservative wherever opportunity presents. Do you know of proof to the contrary?

 

[MXGratefulDiver]

DanV,

We do see this differently. Here's my take on your risk management algorithm:

DCS - no BIG risk, ergo... no risk at all

[-]OAA[/-] less than excess reserve at the surface - some (unspecified) HUGE risk, so this dominates once some minimum time for off-gassing is satisfied.

I hope new divers will quickly figure out that they can safely address both, and to what extent reserving gas is needed for their safety.

I'm no expert on the state of DCS understanding but the stuff you mention that implies any precision or accuracy to the foreseeability of personal risk does not fit with what I do (think I) know. Though I'm sure I'm not doing it justice, my take is that the current models come from "start with 1% acute clinical DCS risk, take a step or two to the happy side, throw in some animal and tissue studies of difficult-to-place relevance, a lot of pontificating and presumptive tweaking, express it precisely so it seems definitive, and there you have it". Virtually no data on lesser endpoints than acute DCS. That doesn't give me much confidence that the entire exposure space between there and never crossing below the surface is properly or prudently defined as 'safe', meaning without adverse consequence. It seems there's plenty of evidence that could mean a continuum and even accumulation of the harm, and to my logic that means shade to the conservative wherever opportunity presents. Do you know of proof to the contrary?

I believe it was Ross Hemingway who put it most appropriately regarding decompression ... "We're all lab rats". That's a simple summation of the fact that there's just too many variables to come up with anything resembling hard and fast rules that apply in all cases.

That said, I think you've been either mistaking Dan V's comments or using them to set up strawman arguments. I don't think Dan has said or intended to say that safety stops should be taken lightly. I read him as saying that if you have to make a choice between DCS or OOA, DCS is fixable ... death is not. Therefore, don't get so fixated on the safety stop that you run yourself out of air and therefore put yourself in an even worse place ... because in any case, running out of air greatly increases your risk of a bad outcome.

I'm a firm believer in the concept that the best divers are those who don't put themselves in a situation to have to make that decision ... and a good foundation in gas management will give most divers a better set of tools to achieve that goal. But if you should find yourself in a position to have to make that choice, choose the lesser of two evils ... which in this case would be to surface before your air supply runs out.

... Bob (Grateful Diver)

 

[Thalassamania]

Sorry to the people who think it's cool to do a cesa, but there are plenty of divers that have hundreds of dives and have never had the need for them. Be responsible.

No one is suggesting that an ESE is "cool," merely that with what we think is adeaquate training, it's no BFD.

Thal,
Speaking of all the new electronics which will alert for low air supply....
Here is a picture for you....diving on a chater boat with 15 divers, many new....at about 40 minutes into a 55 foot deep dive, most beginning to ascend....you are suddenly aware of a symphony of computer alarms, notifications, and bells and electronic sounds surrounding you....the natural noises of the ocean now replaced with the "Dance of the DEMA Show"....
With all the alarming going on, which ones are suggesting a slower ascent, which ones are suggesting that the NDL will arrive in 5 minutes, which ones are suggesting a diver is low on air, and which ones are proclaiming a tank half full to be empty?

At least with the honking first stage, you had no doubt it was low on air....and the mechanical failure / false warning far less likely than the computer alarming with nonsense the owner does not want it alarming on....

Regards,
DanV

P.s.
I do remember Pat's regulator honk being disconcerting.... I think some people would try hard tp prevent the low on air from happening, so this honking did not scream this out to the world.
Fortunately, Pat Frain was rarely low on air.

I have yet to experience the "Dance of the DEMA Show," but I do get the idea. I wonder how many of the beepers knew if they were beeping and why they were beeping.

I just want to re-emphasize the issues here and attempt to make a distinction between the new(ish) diver and the experienced one regarding safety stops and being low on air.

While I wish I had the time and committment from all of my Open Water students to faithfully practice their various skills once every couple of weeks after they have been certified, the REALITY is that I will be lucky to have 10% of them even do a dive once every 6 months after being certified (and taking the trip that prompted the class). I'm sorry Thal, Dan, Bob, et al, but I'm just not that good enough of an inspiration as an instructor to get them to do this -- dive AND practice their diving skills.

Thus, MY HOPE is that they learn, and retain, enough to be safe throughout their dive AND THAT IF/WHEN they screw up they get to the surface as quickly as safely possible (and that is actually pretty darn quick). I don't want them screwing around, getting possibly panicked, waiting for that last hard breath (been there, done that -- and I wish J-valves were still in use) -- I just want them ON THE SURFACE while being able to breathe normally all the way up. AND once on the surface, they have a sufficient supply of air to inflate their BC/Wing so that they STAY ON THE SURFACE.

In the PNW, we've had way too many deaths "due to drowning" which, in reality, were due to being OOA for in each of the three (at least) cases the victim was able to get to the surface. But, sadly, they had no air left and couldn't power inflate their BCs and orally inflating (and/or dumping their weights) left them in the panic resulting from being OOA.

Yes, Dan V and Thal have the skills necessary to run out of air at 100 FSW and then calmly doing a free ascent AND then calmly finding their inflator hose, press the right button and calmly inflate their wings. Unfortunately, the students I seem to have trained (and those I have seen) just don't have those skills -- perhaps because I'm a rotten instructor or, just perhaps, because, well, you may be able to determine other reasons.

In any event, for THE VAST MAJORITY OF BASIC OPEN WATER DIVERS, if they are low on air, the safest place is ON THE SURFACE -- and the sooner the better. At least that is what this poor, inexperienced, lowly PADI instructor believes.

Peter, it is not you as an instructor, it is the curriculum that you choose to teach that results in divers who lack what Dan and I see as essential training. I choose not to teach that curriculum, Dan wants nothing to do with it either, and sure, that places us out of the current mainstream of diving instruction. But that does not make mainstream instruction adequate to the tasks faced since it is a serious compromise of the skills needed for local diving in favor of the skills that may not be needed in escorted resort diving. I don't see that it is all the difficult to impart to students the where-with-all to be able to run out of air at 100 FSW and then calmly doing a free ascent AND then calmly finding their inflator hose, press the right button and calmly inflate their wings. Those skills strike me as defining a competent diver and are what we all should be able to expect, but can't. Again, the problem is the individual instructor, but (as we have noted with so many other items, such gas gas management planing, buoyancy and trim, decompression theory, etc.): it is the curriculum that is used.

I'll repeat what I posted earlier from Karl Huggins, Director of the Catalina Hyperbaric Chamber and a noted expert in the field: Decompression sickness (bends/DCS) rarely kills anyone.

AGE (embolism) is definitely life-threatening and frequently results from an OOA incident that produces a rapid ascent (doesn't have to be panicked . . . but frequently is) where either the diver holds their breath on ascent or doesn't exhale properly/enough on the way up.

AGE often kills. DCS rarely kills.

Draw whatever conclusions you want from that.

- Ken

I've thought about this a lot of the weekend, and reached the same conclusion. Item one is getting the diver back to the surface with at least enough air to establish stable, positive buoyancy. Item two is being able to make a comfortable and competent ESE. But I still think that BOTH are hallmarks of an adequately trained diver.

For a great many new divers, 500 psi at 60 feet down will be almost gone by the time they are 1 minute into their 15 foot stop. For these divers, a serious risk is OOA.
DCS from a 60ft for 45 min dive should not be a risk if they just swim up slowly with no stop. On one hand we have a big risk. On the other, we do not.
I don't see how this makes my posting seem single minded...

The tables a new diver will use, are extremely conservative....so much so, they could actually cause a dramatic increase in danger for a fit technical diver....there is so much fudging tossed in for low fitness levels and PFO issues, that they can make a fit diver have to do deco for his deco....ie, drastically less time should be spent by this diver at most stops on deep dives of long duration.
Point being, your individual off gassing is your big issue to learn...
If I am going to give advice on this issue here, it is the dcs issue is small risk to the 75 percent of divers with no PFO.....for the 25 percent that does have a pro, your medical problem should not have been figured into the tables, compromising the people without pro's. I would like much more individualized tables for divers, like what the WKPP has, but that won't be happening.....


Also.....

Who is teaching that safety stops are mandatory? When you have lots of air, they are smart. When you are really low on air, they are not related to safety anymore.

Regards
DanV

With divers now slowing their ascents to an actual 30 fpm, as opposed to a maybe 60fpm (that was often 120+ fpm!) the SS now serves more as a way to get a diver to take control and gently surface rather than accelerate through the last 20 feet. I think that we should stop teaching safety stops and start teaching control stops. Come to a halt at 20 feet and S-L-O-W-L-Y and in control proceed to the surface. Kinda a different concept.

 

[Scott L]

With divers now slowing their ascents to an actual 30 fpm, as opposed to a maybe 60fpm (that was often 120+ fpm!) the SS now serves more as a way to get a diver to take control and gently surface rather than accelerate through the last 20 feet. I think that we should stop teaching safety stops and start teaching control stops. Come to a halt at 20 feet and S-L-O-W-L-Y and in control proceed to the surface. Kinda a different concept.

Does anybody have the George Irvine's (GUE) position paper on this subject? It hit on this issue quite a bit. I will get from Cave Diver or Deepstops if need be...

 

[Thalassamania]

Please post it (or a summary).

 

[danvolker]

DanV,

We do see this differently. Here's my take on your risk management algorithm:

DCS - no BIG risk, ergo... no risk at all

[-]OAA[/-] less than excess reserve at the surface - some (unspecified) HUGE risk, so this dominates once some minimum time for off-gassing is satisfied.

Spoolin,
I am not thrilled at the way you are twisting my words..... I tried to make it abundantly clear that the issue of DCS not being an issue, was with a slow continuous ascent to the surface on a dive fitting No Stop / NDL parameters...I even shortened the duration by 5 minutes in my example...

I am beginning to think your instructor trained you to believe that DCS is some insideous threat, ready to pounce on you the moment you exceed your table by a second or two--or the moment you miss a "SAFETY STOP". If this is the case, you need a fresh perspective. I'm sure Thal or Bob or Peter can explain this in a more traditional manner, but you need to look at how bubbles form in your body durring a dive, and how well most bodies get rid of the bubbles as you ascend ( and later on the surface) ... There was a time the George Irvine, Bill Mee, myself and a few others had a Doppler study done [on us, or for us --?? ] , and the objective was to show how quickly our personal physiologies were able to deal with what "should" have been hypersaturation, according to the typical PADI tables...
We did a 125 foot dive, for about 27 minutes. It was a high crusiing speed dive, a spearfishing dive for me, the other guys keeping pace. They wanted us to do an ascent with no stop, just 60 foot per minute climb to surface--then get out, and get dopplered. And then again in about 15 and then 30 minutes.
Again. No Deco stop. No Safety stop.


< note to Spoolin......this is considerably beyond the 60 foot dives with 45 min duration, and my suggestion for blowing off the stop if very low on air>


UNique for my situation, was that I had been in a bicycle race crash 4 days earlier, and had almost separated my shoulder--not quite, but there was still swelling and the expectation was that blood flow would be compromised, and this would hurt offgassing/lead to more bubbling in the area of my shoulder.
Also unique, was my speargun..a huge 60 inch double barrel Ultimate Speargun made by Pat Frain, it was nearly as heavy as a Nato Assault Riffle. This I had no concerns over at all...but....
most of us had minor bubbling, nothing of any concern at all...when they did my injured shoulder, I expected the doppler to show some serious bubbling..but it was completely insignificant...however, the arm holding my speargun throughout the dive was bubbling at a considerably significant level..not enough for me to want to administer O2, but clearly, having a heavy muscle load throughout a dive like this, leads to very constricted muscles, meaning poor blood flow, meaning bubbling will become a problem...in recreational diver "speak", if you are pushing a big two strobe housed camera around, you are getting bubbling issues far beyond your evel twin without a camera....this could easily explain the arthritis seen in many of the older big name photographers ...
In any event, even my speargun arm cleared fast in the first 15 minutes, once the muscle constriction was over.

The point of this big story, is that a group of us, all into cardio sports outside of diving, could on a given day, blow the daylights out of the tables, and not have it maim or kill us.
Bubble theories give divers with math backgrounds ideas on how to prevent DCS.
Each day I go out, I have a table based plan for my dives....and I take the plan seriously. That being said, if my buddy needs to come up because of an emergency, I KNOW that I can blow off huge parts of a real deco dive, and still survive or have even no bad effects--and to save your buddy, this is the behavior to utilize. On a No Stop/No Deco dive, I think this point should have been well "overstated"

Regards,
DanV

 

[lamont]

DanV,

We do see this differently. Here's my take on your risk management algorithm:

DCS - no BIG risk, ergo... no risk at all

That isn't what Dan is saying.